1. Field of the Invention
The invention relates generally to induced polarization prospecting methods and, more particularly, but not by way of limitation, it relates to an improved data evaluation system wherein complex resistivity of the earth's substructure is established to provide more definitive output indication.
2. Description of the Prior Art
The prior art includes numerous types of induced polarization systems, many basic types of which have been utilized in geophysical prospecting for a number of years. Field techniques have not changed greatly since the first induced polarization survey was run except that equipment has been vastly improved, becoming more compact, more reliable, and more sensitive; however, induced polarization still utilizes basically the same type of field array as is used in general resistivity survey and such resistivity survey has been practiced since about 1920.
In the field, there are presently practiced two basic types of induced polarization surveying, i.e. time domain and frequency domain surveying. In time domain practice, the method entails pulsing the ground with a symmetrical wave form which is 50% on/off, on times varying from two to ten seconds with equal off times. In this method, the measured parameters of interest are the areas under the established discharge curves from which additional parameters as to chargeability may be obtained. In the frequency domain method IP measurements are made at two different frequencies, usually a decade apart, with measurement of a parameter equal to the steady state voltage response which is then reduced to the frequency effect parameter, well known in IP survey data analysis. None of the presently employed techniques provide data indicating other than near-anomalous regions and thus far it has not been possible to make deterministic measurements utilizing the known IP methods.